Add an environment variable EMSCRIPTEN_ROOT for emscripten installed with brew and add supports for other wasm targets.

z3-sys/README.md

@@ -51,6 +51,15 @@ There are 3 ways for this crate to currently find Z3:
   by that version to be used. In this case, there is no override
   via the environment variable.
 
+### Finding emscripten
+
+For wasm32 targets, we may need an existed emscripten installation for a `sysroot`.
+One may specify the root of emsdk by environment variable `EMSDK`,
+or the root of emscripten by environment variable `EMSCRIPTEN_ROOT`.
+Then we'll use `$EMSDK/upstream/emscripten/cache/sysroot` or `$EMSCRIPTEN_ROOT/cache/sysroot`.
+
+For example, if you're using brew, you can assign `$HOMEBREW_CELLAR/emscripten/<emscripten version>/libexec` to `EMSCRIPTEN_ROOT`.
+
 ## Support and Maintenance
 
 I am developing this library largely on my own so far. I am able

z3-sys/build.rs

@@ -102,11 +102,22 @@ fn generate_binding(header: &str) {
             .generate_comments(false)
             .rustified_enum(format!("Z3_{x}"))
             .allowlist_type(format!("Z3_{x}"));
-        if env::var("TARGET").unwrap() == "wasm32-unknown-emscripten" {
-            enum_bindings = enum_bindings.clang_arg(format!(
-                "--sysroot={}/upstream/emscripten/cache/sysroot",
-                env::var("EMSDK").expect("$EMSDK env var missing. Is emscripten installed?")
-            ));
+        let target = env::var("TARGET").unwrap();
+        let wasm = target.starts_with("wasm");
+        let emscripten = target.ends_with("emscripten");
+        if wasm {
+            // It seems that sometimes the cache may be missing.
+            let sysroot = env::var("EMSDK")
+                .map(|emsdk| format!("{}/upstream/emscripten/cache/sysroot", emsdk))
+                .or_else(|_err| {
+                    env::var("EMSCRIPTEN_ROOT")
+                        .map(|emscripten_root| format!("{}/cache/sysroot", emscripten_root))
+                });
+            if let Ok(sysroot) = sysroot {
+                enum_bindings = enum_bindings.clang_arg(format!("--sysroot={}", sysroot));
+            } else if emscripten {
+                panic!("$EMSDK and $EMSCRIPTEN_ROOT env var missing. Is emscripten installed?");
+            }
         }
         enum_bindings
             .generate()